"It's gone so quickly," Zara, who is currently in Australia in her role as an ambassador for Magic Millions races, told Daily Mail Australia.
The 33-year-old is preparing to celebrate Mia's first birthday
The 33-year-old went on to reveal that she hasn't yet planned anything for Mia's first birthday on 17 January, saying: "[I've] got to go home first and then see what happens."
The Exeter University graduate added that Mia enjoys playing with her fellow royal youngsters, including Prince George and her cousins Savannah and Isla.
"We've all got small ones now," she said. "So it's great fun."
Zara was in Queensland for the racing event
Zara's comments came on Saturday when she stepped out at Gold Coast Racecourse in Queensland to award the winner of the Racing Women prize.
The Queen's granddaughter, whose husband Mike Tindall is currently training to take part in Channel 4's The Jump, has been enjoying her time Down Under.
"It's just fantastic," said Zara, who is set to return to Australia every year until 2018. "It's going to be great to come back down every year and get a bit of sunshine."
Zara and Mike introduced baby Mia to HELLO!
Once she's returned to England, however, it's time for Zara to get back to training her horses.
"I'll be getting all the training going again," she said. "Start a new season."